#!/usr/bin/env python3
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#    Copyright (C) 2016 Jose A. Rivera <jarrpa@samba.org>
#    Copyright (C) 2016 Ira Cooper <ira@samba.org>
"""CTDB mutex helper using etcd.

This script is intended to be run as a mutex helper for CTDB. It will try to
connect to an existing etcd cluster and grab an etcd.Lock() to function as
CTDB's cluster lock. Please see ctdb/doc/cluster_mutex_helper.txt for
details on what we're SUPPOSED to be doing. :) To use this, include
the following line in the ctdb.conf:

    cluster lock = !/path/to/script

You can also pass "-v", "-vv", or "-vvv" to include verbose output in the
CTDB log. Additional "v"s indicate increases in verbosity.

This mutex helper expects the system Python interpreter to have access to the
etcd Python module. It also expects an etcd cluster to be configured and
running. To integrate with this, there is an optional config file of the
following format:

key = value

The following configuration variables (and their defaults) are defined for
use by this script:

port      = 2379   # connecting port for the etcd cluster
lock_ttl  = 9      # seconds for TTL
refresh   = 2      # seconds between attempts to maintain lock
locks_dir = _ctdb  # where to store CTDB locks in etcd
                   # The final etcd directory for any given lock looks like:
                   #   /_locks/{locks_dir}/{netbios name}/

In addition, any keyword parameter that can be used to configure an etcd
client may be specified and modified here. For more documentation on these
parameters, see here: https://github.com/jplana/python-etcd/

"""
import signal
import time
import sys
import os
import argparse
import logging
import subprocess

import etcd

# Helper Functions ------------------------------------------------------------
#


def process_args():
    '''Process command-line arguments and return them.
    '''
    parser = argparse.ArgumentParser(
        description=__doc__,
        epilog='',
        formatter_class=argparse.RawDescriptionHelpFormatter)
    parser.add_argument('-v', '--verbose',
                        action='count',
                        help='Display verbose output to stderr. '
                             'Default is no output.',
                        default=0,
                        )
    parser.add_argument('-c', '--config',
                        action='store',
                        help='Configuration file to use. The default behavior '
                             'is to look is the base CTDB configuration '
                             'directory, which can be overwritten by setting '
                             'the CTDB_BASE environment variable, for a file '
                             'called \'etcd\'.  Default value is %(default)s.',
                        default=os.path.join(os.getenv('CTDB_BASE',
                                                       '/usr/local/etc/ctdb'),
                                             'etcd'),
                        )
    args = parser.parse_args()

    return args


def setup_logging(verbose):
    '''Setup logging based on specified verbosity.
    '''

    log_levels = [logging.ERROR, logging.WARNING, logging.DEBUG]
    logging.basicConfig(level=log_levels[min(verbose, len(log_levels)-1)])


def sigterm_handler(signum, frame):
    """Handler for SIGTERM signals.
    """
    sys.exit()


def print_nonl(out):
    """Dumb shortcut for printing to stdout with no newline.
    """
    sys.stdout.write(str(out))
    sys.stdout.flush()


def int_or_not(s):
    """Try to convert input to an integer.
    """
    try:
        return int(s)
    except ValueError:
        return s

# Mainline --------------------------------------------------------------------
#


def main():
    args = process_args()

    setup_logging(args.verbose)

    # etcd config defaults
    etcd_config = {
        'port': 2379,
        'locks_dir': '_ctdb',
        'lock_ttl': 9,
        'lock_refresh': 2,
    }
    # Find and read etcd config file
    etcd_client_params = (
        'host',
        'port',
        'srv_domain',
        'version_prefix',
        'read_timeout',
        'allow_redirect',
        'protocol',
        'cert',
        'ca_cert',
        'username',
        'password',
        'allow_reconnect',
        'use_proxies',
        'expected_cluster_id',
        'per_host_pool_size',
    )
    if os.path.isfile(args.config):
        f = open(args.config, 'r')
        for line in f:
            (key, value) = line.split("=", 1)
            etcd_config[key.strip()] = int_or_not(value.strip())

    # Minor hack: call out to shell to retrieve CTDB netbios name and PNN.
    tmp = subprocess.Popen("testparm -s --parameter-name 'netbios name'; \
                          ctdb pnn",
                           shell=True,
                           universal_newlines=True,
                           stdout=subprocess.PIPE
                           ).stdout.read().strip()
    nb_name, pnn = tmp.split()

    # Try to get and hold the lock
    try:
        client = etcd.Client(
            **{k: etcd_config[k] for k in
               set(etcd_client_params).intersection(etcd_config)})
        lock = etcd.Lock(client, etcd_config['locks_dir'] + "/" + nb_name)
        lock._uuid = lock._uuid + "_" + pnn
        logging.debug("Updated lock UUID: %s", lock.uuid)
        ppid = os.getppid()
        while True:
            lock.acquire(blocking=False, lock_ttl=etcd_config['lock_ttl'])
            if lock.is_acquired:
                print_nonl(0)
            else:
                locks = "No locks found."
                if logging.getLogger().getEffectiveLevel() == logging.DEBUG:
                    keys = client.read(lock.path, recursive=True)
                    if keys is not None:
                        locks = "Existing locks:\n  "
                        locks += '\n  '.join(
                            (child.key + ": " + child.value for child in
                             keys.children))
                logging.debug("Lock contention. %s", locks)
                print_nonl(1)
                break
            os.kill(ppid, 0)
            time.sleep(etcd_config['lock_refresh'])
    except (OSError, SystemExit):
        if lock is not None and lock.is_acquired:
            lock.release()
    except Exception:
        print_nonl(3)
        if logging.getLogger().getEffectiveLevel() == logging.DEBUG:
            raise


if __name__ == "__main__":
    signal.signal(signal.SIGTERM, sigterm_handler)

    main()
